Biological specimens such as tissues and organs that are to be used in transplantation must often be transported over large distances from the donor to the recipient. Currently, most of these tissues and organs are cooled to just above 0.degree. C. and are transported by packing the tissues in ice. When tissues are shipped in this manner, the viability of the tissue can be maintained at an acceptable level only for a short period of time. If the tissues are not used within several hours after removal from the donor, the tissue will begin to deteriorate and will no longer be usable as a transparent tissue or organ.
Another method of preparing tissues for transport is by first freezing the tissue and then lowering the temperature of the tissue to super cold temperatures lower than -190.degree. C. This is commonly done for heart valves. Freezing transplanation tissues offers many advantages over cooling tissues to near 0.degree. C. The tissues can be tested for compatability andd then stored in supercold refrigerators in tissue banks until they are needed. In this way, a tissue is immediately available when it is needed. However, the frozen tissue must still be transported as rapidly as possible since the recipient may only have a limited amount of time within which the tissue can be transplanted.
Rapidly transporting tissues at supercold temperatures presents certain problems. The most common method of maintaining supercold temperatures is through the use of liquid nitrogen. The boiling point of nitrogen is -195.8.degree. C. In addition, nitrogen is non-toxic. However, as nitrogen warms, it is transformed into a gas and escapes into the atmosphere. Thus, conventional methods of transporting tissues at supercold temperatures utilize specially constructed bottles that are well insulated. However, because these bottles are sealed there is a danger that the nitrogen will warm up and will transform into a gas. If the container is sealed, there is great danger of an explosion. As a result of this danger, transportation of liquid nitrogen is highly regulated. In fact, transportation of liquid nitrogen-containing vessels on commercial airlines is prohibited in some countries.
Thus, frozen tissues and organs that must be maintained in a frozen state in liquid nitrogen must be shipped by special carrier. This increases the time and cost of shipping these types of biological specimens.